Add a lock around the SPI bus

This seems to have been the cause of recurring deadlocks that have been
difficult to repo.

3 files changed, 15 insertions, 2 deletions

diff --git a/src/drivers/display.cpp b/src/drivers/display.cpp
index 48310074..a06320f4 100644
--- a/src/drivers/display.cpp
+++ b/src/drivers/display.cpp
@@ -34,6 +34,7 @@
 #include "gpios.hpp"
 #include "misc/lv_color.h"
 #include "soc/soc.h"
+#include "spi.hpp"
 #include "tasks.hpp"
 
 static const char* kTag = "DISPLAY";
@@ -267,8 +268,12 @@ void Display::SendTransaction(TransactionType type,
 
   gpio_set_level(kDisplayDr, type);
 
-  // TODO(jacqueline): Handle these errors.
-  esp_err_t ret = spi_device_transmit(handle_, &sTransaction);
+  esp_err_t ret;
+  {
+    auto lock = drivers::acquire_spi();
+    // TODO(jacqueline): Handle these errors.
+    ret = spi_device_transmit(handle_, &sTransaction);
+  }
   ESP_ERROR_CHECK(ret);
 }
 
diff --git a/src/drivers/include/spi.hpp b/src/drivers/include/spi.hpp
index 7dbc2aae..60638f71 100644
--- a/src/drivers/include/spi.hpp
+++ b/src/drivers/include/spi.hpp
@@ -6,11 +6,13 @@
 
 #pragma once
 
+#include <mutex>
 #include "esp_err.h"
 
 namespace drivers {
 
 esp_err_t init_spi(void);
 esp_err_t deinit_spi(void);
+std::lock_guard<std::mutex> acquire_spi(void);
 
 }  // namespace drivers
diff --git a/src/drivers/spi.cpp b/src/drivers/spi.cpp
index 93bf9cde..ba461b67 100644
--- a/src/drivers/spi.cpp
+++ b/src/drivers/spi.cpp
@@ -20,6 +20,8 @@ static const gpio_num_t kSpiSdoPin = GPIO_NUM_23;
 static const gpio_num_t kSpiSdiPin = GPIO_NUM_19;
 static const gpio_num_t kSpiSclkPin = GPIO_NUM_18;
 
+static std::mutex sSpiMutex{};
+
 esp_err_t init_spi(void) {
   spi_bus_config_t config = {
       .mosi_io_num = kSpiSdoPin,
@@ -52,4 +54,8 @@ esp_err_t deinit_spi(void) {
   return spi_bus_free(kSpiHost);
 }
 
+std::lock_guard<std::mutex> acquire_spi(void) {
+  return std::lock_guard<std::mutex>{sSpiMutex};
+}
+
 }  // namespace drivers